From Your Shopping Cart To The Ocean Garbage Patch Impact

An object enters the North Pacific Ocean off the California coast. It could be a plastic bag, nylon line, a plastic toy, an article of clothing, or some of that annoying plastic packaging that at one time contained a cell phone or shaving kit. Perhaps it had floated down a river, been washed through a storm drain, swept from a beach, or tossed from a ship.

Once adrift, onshore winds may push it back on land. But more likely it will get swept up in the subtropical gyre, the great loop formed by the California, North Equatorial, Kuroshio, and North Pacific currents. Objects caught in the gyre may circle it many times, traveling from California west towards the Philippines, north to Japan, then east again to California. Each 14,000 nautical mile orbit takes about 6.5 years to complete. Seasonal onshore winds may dislodge it from these currents and deposit it back on land. There it may get buried in sand, collected by a beachcomber, or most likely swept out to sea again.

Floating Refuse Comes Home

Marine debris on Hawaiian coast. NOAA

Winds may push the object inside the gyre. There it may drift into an area between California and Hawaii where the winds stagnate and currents become chaotic. It may remain trapped for years, decades, or perhaps centuries before a chance wind washes it up onto a nearby island or pushes it back out into the currents of the gyre. Over time, the sun and waves may break down the non-biodegradable components into smaller and smaller pieces, some barely the size of grains of sand. But the plastic never disappears.

The object would have plenty of company. Floating refuse of all types from countries rimming the gyre cover this vast patch of the North Pacific. This enormous trash repository, where according to some measurements the confetti-like plastic pellets outweigh the plankton six to one, is now known as the Great Eastern North Pacific Garbage Patch.

Researchers predict that there are as many as eight garbage patches within the ocean’s five subtropical gyres, each of which concentrates the massive volumes of trash released into the ocean every year. But so far they have only confirmed presence of the one in the eastern North Pacific and in the western North Atlantic. Basic questions remain. Where are garbage patches located? How much and what type of debris do they contain? What are the meteorological and oceanic forces that shape them? And what are the environmental impacts?

Ebbesmeyer Tracks Floating Debris

The moniker “garbage patch” was coined by Curtis Ebbesmeyer, a retired oceanographer and expert on ocean currents. He calls garbage patches “one of Earth’s most important geological features,” and marvels that until now nobody has taken much notice. “It’s as if the planet Mars was orbiting right with the Moon, but we never saw the planet. It’s that obvious!”

Ebbesmeyer’s interest in garbage patches is built on two decades spent tracking the journeys of floating debris. His objects of study have most famously included fleets of Nike sneakers and plastic bath toys that had spilled off

cargo ships into the North Pacific. They also have included an exhaustive list of anything that floats, including glass bottles, glass fishing floats, clay jars, sandals, surfboards, and even corpses.

Ebbesmeyer has tracked these objects with the help of his friend Jim Ingraham of the Alaskan Fisheries Service. Ingraham has developed a computer model of the NorthPacific currents called the Ocean Surface Currents Simulator (OSCURS). It is based on data on ocean currents and meteorological conditions that naval ships have gathered daily. If Ebbesmeyer and Ingraham can figure out where and when an object’s journey began and ended, then OSCURS can calculate the path it took in between. Most of the data they have gathered has come courtesy of a world-wide network of beachcombers, and over the years it has enabled Ingraham to refine OSCURS to the point where it can reliably predict the paths of objects dropped in the ocean.

Their work has revealed much about the behavior of objects entering gyres. They have observed that objects circle the edges of the gyres, often many times, before washing back up on shore. The dynamics of the garbage patches still remain murky, however. Simulations run on OSCURS show objects becoming entrapped in areas corresponding to the garbage patches. But Ebbesmeyer says that the transfer from gyre currents to garbage patch appears random, and is not well understood.

Modeling Garbage Patches

Simulation of evolution of drifter density (or marine debris): (a) from an initially homogeneous state, (b) after one year, (c) after 3 years, (4) after 10 years of movement by currents, as determined from real drifter movements. Units represent relative change in drifter concentration.

The model shows that the drifters tend to collect in five regions.
These regions correspond to the centers of the five subtropical gyres. Maximenko, International Pacific Research Center

Nikolai Maximenko, a Senior Researcher at the International Pacific Research Center at the University of Hawaii, has constructed a model that shows the pull of garbage patches in even more dramatic fashion. His model is based on the movements over five days of 12,000 satellite-tracked drifters that had been released worldwide as part of NOAA’s global drifter program. Maximenko divided the ocean up into grids of squares called bins and calculated the probabilities that drifters occupying each bin would move into each one of the adjacent bins. Then he ran simulations based on these probabilities in which he released virtual drifters and tracked them for up to one thousand years. The model showed that after ten years, the density of drifters
increased significantly in five regions of the subtropical ocean. The two most dramatic increases took place in the area corresponding to the North Pacific garbage patch and in the eastern South Pacific.

The potential garbage patches that both Ebbesmeyer and Maximenko have identified sit beneath large subtropical high-pressure systems. These high-pressure systems are the likely driving forces that create the garbage patches. The high pressure systems form from the warm moist air that rises above the equator, diverges towards the poles, then after losing heat and moisture, sinks at about 30 degrees north and south. (Much of the air then speeds back towards the equator, creating the trade winds. These closed loops of air circulating between the equator and subtropics are called Hadley cells.) As air moves away from these subtropical highs, Earth’s rotation (the Coriolis effect) deflects it so that it rotates around the high pressure systems; clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. These rotating winds create ocean currents. The Coriolis effect then steers the ocean currents back towards the high-pressure systems (Ekman transport). It is these currents that carry the debris into the garbage patch.

Once beneath the high-pressure systems, the floating debris appears to meander aimlessly. Ebbesmeyer says that shifting winds occasionally dislodge a chunk of debris, much of it plastic that has been broken down into confetti-sized plastic bits, and pushes it on shore. These massive deposits of trash fouling the beaches are boons to beachcombers since they often contain objects that have been afloat for decades. But they are a stark reminder of the tremendous volumes of trash floating in the ocean.

The fact that garbage patches are located beneath high-pressure systems also helps explain why it took so long for people to notice them. These areas are notorious for their calm winds, so sailors avoid them. The tiny plastic pellets that make up the bulk of the debris are practically invisible to crews of freighters that pass through. Airplanes and satellites can’t detect them at all.

Ebbesmeyer and groups such as the Algalita Marine Research Foundation in Long Beach, Calif., are now spreading the word about garbage patches and their potential environmental impact. Algalita is funding expeditions into the South Atlantic and the Sargasso Sea, a region of the North Atlantic famous for its dense mats of seaweed.

The Sargasso Sea

The Sargasso Sea, Courtesy of the U.S. Fish and Wildlife Service

Researchers are discovering that the Sargasso Sea may in fact contain densities of plastic similar to those found in the eastern North Pacific garbage patch. For the last 22 years, students at the Sea Education Association (SEA) in Woods Hole, Mass, have used plankton nets to scoop up plastic from the western North Atlantic. (SEA offers college students semester-long oceanography courses that include six-week research cruises.) Kara Lavender Law, a physical oceanographer at SEA, has been working on compiling these data so she can map the distribution of the plastic and examine how densities may have changed over time. She says that locations of the highest densities of plastic almost exactly matches those predicted by Maximenko’s ocean currents model.

In the summer of 2010, SEA will send a research cruise back into the Sargasso Sea to collect plastic from areas that have not yet been sampled. They will use Maximenko’s model as a guide to where to look. These data should help them further define the boundaries of the garbage patch.

It is in the eastern South Pacific, however, that Maximenko’s model predicts the most powerful convergence and therefore perhaps the largest garbage patch. To begin exploring this area, Maximenko and his colleagues have sought the help of Jim Mackey, an adventure sailor who is attempting a solo circumnavigation of the ocean. They are providing Mackey with navigational data and equipment for sampling plastic carried from countries rimming the South Pacific.

Assessing the potential environmental hazards posed by these dense concentrations of floating debris is an especially daunting task. Researches have documented numerous incidences of marine mammals, reptiles, and birds entangled in abandoned fishing gear or choking on plastic bags. But it is the high concentrations of tiny plastic pellets that could potentially alter ecosystems.

Around the world, plastic pollution has become a growing plague. In this video Dr. Marcus Eriksen sailed a vessel named "Junk" made out of plastic bottles from LA to Hawaii to research the problem and raise awareness.

Learn more at 5gyres.org

In the summer of 2009, Miriam Goldstein, a graduate student studying biological oceanography at the Scripps Institute of Oceanography in La Jolla, Calif., led a research cruise of fellow graduate students into the eastern North Pacific garbage patch to sample the plastic and study its impact. What the students saw surprised them. One hundred consecutive quarter-mile long plankton tows over 1,700 miles of ocean yielded plastic. Goldstein said it was crazy. “Every time we put a plankton net in, we would find these tiny pieces of plastic that looked like confetti or a snow globe.”

The student researchers addressed a wide variety of questions about the plastic’s impact. Of great concern is the extent to which organisms, from birds to fish to zooplankton, ingest the tiny plastic grains. Studies have shown that Laysan albatross chicks, especially those hatched near a garbage patch in the western North Pacific, have consumed large quantities of plastic. Researchers have also found plastic in the guts of some fish species.

Biologists fear that the plastic may interfere with digestion by clogging the gut or by simply replacing real food and the nutrition it provides. Some plastics may contain toxins. Other plastics may absorb and therefore concentrate toxins from the surrounding water. Theoretically, these toxins could then get passed up the food chain as predators devour the consumers. Given our taste for large predators such as tuna, the toxins could perhaps reach our dinner plates.

Other potential impacts of the plastic are less direct. Goldstein is investigating the extent to which invertebrates such as crabs, shellfish larvae, and barnacles hitch rides on the plastic to parts of the ocean where they are normally not found. The introduction of new species to an area can sometimes change an ecosystem by suppressing native species or altering the food web. Even bacteria colonizing the floating plastic can alter the flow of nutrients in the water.

Goldstein says that the cruise participants are now back in the lab engaged in the time-consuming processes of sorting through the plastic they recovered, dissecting fish, and identifying and cataloging the organisms found on the plastic.

For years, garbage patches, for all their enormity, have remained out of sight. Through the efforts of these scientists and environmental organizations, the scope of the threat that garbage patches pose is just beginning to enter the public’s conscience. Unraveling the interplay between weather patterns and ocean currents that create theses garbage patches remains a daunting challenge. So does unraveling the impact of the plastic on the complex marine ecosystems. The scientists are ready to meet the challenge. The question is whether the world that produces and throws away so much plastic is also ready.